Electric switches



March 17, 1959 2,878,338

ELECTRIC SWITCHES Filed Feb. 21, 1955 United dtes ELECTRIC SW IT (TEES Frederick Dennis Grihhle, Carshalton, England, assignor to Rotax Limited, London, Engiand This invention relates to electric switches of the kind required to become operative under a persistent exceptional condition, such as an overload, but to be irresponsive to a transient condition, the desired action being under the control of a dash pot and a variable inductance.

A known device in a switch of the kind aforesaid comprises an electromagnet having a spring-loaded armature adapted to effect opening or closing of the switch con tact pieces, and a spring-loaded iron core slidable in a cylindrical bush where it serves to provide a dash-pot elfect and also to vary the inductance of the electromagnet. The arrangement is such that when a persistent current of a predetermined value flows in the electromagnet winding, the core moves against the action of the associated spring at a controlled rate and so as to increase the inductance, until a sutficient magnetic flux is produced to actuate the armature. A transient current of corresponding amount is rendered of no efiect by the delaying action of the dash pot.

When a switch of the kind aforesaid is used on an aircraft, acceleration or deceleration of the air-craft may result in undesired movement of the core of the electromagnet as a consequence of the inertia of the core, and so by influencing the inductance While an otherwise ineffective current is passing through the winding cause an undesired actuation of the switch. The object of the present invention is to enable this condition to be obviated in a reliable manner.

The invention compn'ses a switch of the kind aforesaid having two coaxial and spaced slidable cores contained in a cylindrical bush, and loaded by springs situated between and at the opposite ends of the cores, the arrangement being such that the cores are free to move jointly in the bush and in the same direction in response to accelerations or decelerations of a movable body carrying the switch, and consequently without efiect on the inductance of the electromaguet, but are movable towards each other for increasing the inductance in response to the action of a predetermined current.

The accompanying drawing illustrates a switch embodying the invention.

Referring to the drawing, the electromagnet of the switch comprises a winding a mounted on a non-magnetic metal or other bush b which serves as the cylinder of a dash pot. At the ends of the Winding are arranged a pair of iron pole pieces 0, and within the bush are contained two slidable cores which also extend through holes in the pole pieces. The cores d are situated at a convenient distance apart and are of such length that when atnt 2,878,338 iatented Mar. 17, 1959 ice 2 moved towards each other they eiiect the increase of inductance required for actuation of an iron armature c under the action of a predetermined current in the winding. The cores serve also to provide the required dashpot efiect.

Between and at each of the opposite ends of the cores are contained three springs f, g, and the arrangement is such that when subject to accelerations or decelerations, the cores can move jointly in the bush and in the same direction, but when a suflicient current passes in the winding the cores move towards each other for effecting the desired increase of inductance. The movement of the air or liquid to and from the space between the cores may be regulated by any convenient means.

The armature may be arranged in any convenient manner in operative relation to the pole pieces. In the example iliustrated it is pivoted at its centre and adapted at its ends to move towards and away from suitably disposed faces on the pole pieces. The armature is adapted to actuate a movable contact piece h which co-operates with a fixed contact piece 1'. Also it is loaded by a spring j arranged (in this example) to separate the contact pieces.

By this invention immunity against undesired action of the switch under the conditions mentioned is ensured in a very simple manner.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

An electric switch for air-craft to be operative due to an overload but irresponsive to a transient condition such as inertial etiects resulting from acceleration or deceleration of the air-craft, comprising in combination relatively movable contact pieces, an electromagnet having a spring-loaded pivotally mounted armature responsive to the action of the electromagnet for opening and closing the contact pieces, a non-magnetic bush, 8. pair of coaxial and spaced iron cores slidably mounted in the bush and both capable of sliding movement towards each other under the action of the elcctromagnet to increase the inductance of the latter, the cores serving also to provide a dash-pot effect within the bush, loading springs acting on the outer ends of the cores in the direction for moving the cores towards each other, and another leading spring arranged between the cores and serving by its action on the cores to oppose the actions thereon of the electromagnet and the first-mentioned loading springs so that the cores are free to move jointly and in the same direction within the bush in response to inertial effects without affecting the inductance of the electromagnet.

References Cited in the file of this patent UNTTED STATES PATENTS 2,072,932 Wilckens Mar. 9, 1937 2,131,942 Evans Oct. 4, 1938 2,474,742 Kuhn June 28, 1949 2,515,259 OBrien et al. July 18, 1950 2,700,711 Wilckens Ian. 25, 1955' 2,769,058 Wallace et al. Oct. 30, 1956 FOREIGN PATENTS 342,143 Germany Oct. 13, 1921 

